I don't agree with this, provided that your RD has sufficient chain wrap capacity. With proper capacity and chain length, the RD will handle any possible combination of front chainrings and rear cogs. There may be cross-chaining issues, but those can avoided by choosing different gears. Cross-chaining should be avoided, but it should not be catastrophic if you do it enroute to a different gear.

The real risk is when the chain is actually too short to fit around the chainring and the rear cog, and the results can be severe. Trashed RD, bent/broken derailleur hanger, and broken rear spokes - and worse - you winding up on the ground.